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; Conway's Game of Life, based on the work of:
;; Laurent Petit https://gist.github.com/1200343
;; Christophe Grand http://clj-me.cgrand.net/2011/08/19/conways-game-of-life

(ns ^{:doc "Conway's Game of Life."}
 game-of-life)

;; Core game of life's algorithm functions

(defn neighbours 
  "Given a cell's coordinates, returns the coordinates of its neighbours."
  [[x y]]
  (for [dx [-1 0 1] dy (if (zero? dx) [-1 1] [-1 0 1])]
    [(+ dx x) (+ dy y)]))

(defn step 
  "Given a set of living cells, computes the new set of living cells."
  [cells]
  (set (for [[cell n] (frequencies (mapcat neighbours cells))
             :when (or (= n 3) (and (= n 2) (cells cell)))]
         cell)))

;; Utility methods for displaying game on a text terminal

(defn print-board 
  "Prints a board on *out*, representing a step in the game."
  [board w h]
  (doseq [x (range (inc w)) y (range (inc h))]
    (if (= y 0) (print "\n")) 
    (print (if (board [x y]) "[X]" " . "))))

(defn display-grids 
  "Prints a squence of boards on *out*, representing several steps."
  [grids w h]
  (doseq [board grids]
    (print-board board w h)
    (print "\n")))

;; Launches an example board

(def 
  ^{:doc "board represents the initial set of living cells"}
   board #{[2 1] [2 2] [2 3]})

(display-grids (take 3 (iterate step board)) 5 5) </textarea></form>
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